Effects of altered gravity on the liver

Microgravity as experienced during spaceflight affects a number of physiological processes in various organs. However, effects on the liver have yet been poorly documented. Nevertheless, the liver is a metabolically highly active organ involved in carbohydrate metabolism, lipid metabolism and xenobiotic biotransformation. This chapter provides an overview of effects of microgravity on the liver observed in experimental animals during actual spaceflight and upon simulation of microgravity on Earth. These include (i) induction of liver injury and inflammation associated with apoptosis and oxidative stress, (ii) changes in liver carbohydrate metabolism resulting in the onset of a diabetogenic phenotype, (iii) modifications in hepatic lipid metabolism leading to early metabolic dysfunction-associated steatotic liver disease, and (iv) alterations of the hepatic xenobiotic biotransformation machinery. Although most of these observations remain to be fully validated in human, appropriate measures to counteract liver pathogenesis should be considered, especially in view of long-term space missions.